Medial gastrocnemius muscles fatigue but do not atrophy in paralyzed cat hindlimb after long-term spinal cord hemisection and unilateral deafferentation

Tessa Gordon, Neil Tyreman, Luke R. Harris, Victor F. Rafuse

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Abstract

This study of medial gastrocnemius (MG) muscle and motor units (MUs) after spinal cord hemisection and deafferentation (HSDA) in adult cats, asked 1) whether the absence of muscle atrophy and unaltered contractile speed demonstrated previously in HSDA-paralyzed peroneus longus (PerL) muscles, was apparent in the unloaded HSDA-paralyzed MG muscle, and 2) how ankle unloading impacts MG muscle and MUs after dorsal root sparing (HSDA-SP) with foot placement during standing and locomotion. Chronic isometric contractile forces and speeds were maintained for up to 12 months in all conditions, but fatigability increased exponentially. MU recordings at 8–11½ months corroborated the unchanged muscle force and speed with significantly increased fatigability; normal weights of MG muscle confirmed the lack of disuse atrophy. Fast MUs transitioned from fatigue resistant and intermediate to fatigable accompanied by corresponding fiber type conversion to fast oxidative (FOG) and fast glycolytic (FG) accompanied by increased GAPDH enzyme activity in absolute terms and relative to oxidative citrate synthase enzyme activity. Myosin heavy chain composition, however, was unaffected. MG muscle behaved like the PerL muscle after HSDA with maintained muscle and MU contractile force and speed but with a dramatic increase in fatigability, irrespective of whether all the dorsal roots were transected. We conclude that reduced neuromuscular activity accounts for increased fatigability but is not, in of itself, sufficient to promote atrophy and slow to fast conversion. Position and relative movements of hindlimb muscles are likely contributors to sustained MG muscle and MU contractile force and speed after HSDA and HSDA-SP surgeries.

Original languageEnglish
Article number113201
JournalExperimental Neurology
Volume327
DOIs
Publication statusPublished - May 2020
Externally publishedYes

Bibliographical note

Funding Information:
We are grateful for the support of the Canadian Institute of Medical Research and the Network of Centres of Excellence (NCE) for this research and for support of M.P. as a NCE postdoctoral fellow. We also thank the Alberta Heritage Foundation for Medical Research (AHFMR) for their support of T.G. as a Heritage Research Scientist and of V.F.R. and R.L.H. for their studentship awards.

Funding Information:
We are grateful for the support of the Canadian Institute of Medical Research and the Network of Centres of Excellence (NCE) for this research and for support of M.P. as a NCE postdoctoral fellow. We also thank the Alberta Heritage Foundation for Medical Research (AHFMR) for their support of T.G. as a Heritage Research Scientist and of V.F.R. and R.L.H. for their studentship awards.

Publisher Copyright:
© 2020

ASJC Scopus Subject Areas

  • Neurology
  • Developmental Neuroscience

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